When performing a lateral or anterolateral corpectomy, the diseased or damaged vertebral body and adjacent disc are removed. Removal of the vertebral body and disc leaves a void in the spinal column. Therefore, a vertebral body replacement (VBR) device is placed into the void to provide support to the spinal column. Although the VBR device provides support, the spinal column can still be unstable, particularly in torsion or bending maneuvers. Therefore, surgeons often place a dual rod construct or other stabilization system over the affected level to provide additional stability. In a dual rod construct, pedicle screws are placed in the spine. Two rods are placed into the pedicle screws in parallel arrangement, and locked into the pedicle screws with set screws or other locking mechanisms.
The dual rod construct provides great stability in bending motions, but the spine can still be unstable in response to torsional movement. Therefore, additional devices are needed improve torsional stiffness. Various devices have been developed for rigidly connecting two spinal rods together to increase the stiffness of paired rods. These devices, sometimes referred to as rod to rod connectors, typically feature two or more set screws that must be tightened to connect the device to the rods. Each set screw must be tightened to connect the device to each rod. Tightening set screws can be tedious and time consuming, particularly when multiple rod to rod connectors are being connected to the rods.
U.S. Pat. No. 7,717,938 describes a rod to rod connector that utilizes a single set screw to connect both rods together. The rod to rod connector has an elongate body with two recesses for receiving rods. As the set screw is advanced into the elongate body, the set screw pushes two engagement members outwardly against the two rods. The set screw is advanced until the engagement members lock the rods in the recesses. The single set screw reduces the number of set screws on the connector by one, thereby reducing the amount of time and effort devoted to tightening set screws. Nevertheless, the device has a relatively large footprint due to the transverse width of the assembly. The elongate body must have a center portion large enough to contain not only the set screw, but also the two engagement members in a side by side fashion (see FIG. 1B). This adds to the overall transverse width of the assembly, which is not desirable. The placement of the engagement members inside the central body also limits the axial width of the engagement members, as they can only be as wide as the central body. If the central body is narrow, then the engagement members must be even narrower. If the engagement members are too narrow, they may not grip a large enough area of the rod to securely engage the rod.